"The most characteristic tooth, represented
in figures 7 and 8, plate xxx, supposed to be a premolar, is very unlike the
corresponding teeth, so far as we are acquainted with them, in the distinct
species of Squalodon. The crown of this tooth is subtrihedral conical, as broad
as it is long, ovoid in section at the base, and with a slight twist inwardly.
The inner and outer surfaces are very unequal, and separated by linear, rugulose
ridges. The back of the crown forms, at its basal half, a thick convex tubercle
crossed by the posterior dividing ridge and bounded near the base by a short
embracing ridge. The anterior dividing ridge of the crown pursues a sigmoid
course from the summit postero-internally to the base antero-internally. The
inner and outer surfaces of the crown are conspicuously wrinkled and the former
has, in addition, an irregular curved ridge, terminating in a basal tubercle
and dividing off the anterior more wrinkled third of the inner face of the crown,
from the posterior two-thirds of the same surface. The fang is more than three
times the length of the crown, strongly curved backward, slightly gibbous near
the crown and compressed near the point.
"Length of the crown 6 lines (12 mm.); breadth
6 lines (12 mm.); thickness 4.75 lines (9.5 mm.)" Leidy, 1869.

Description. The species is
"characterized from four molar teeth which were between two and three times
as large as those belonging to Squalodon wymani (Phoca of Leidy)
with similar short incurved crowns, but much more rugose. One molar had a smooth
compressed fang, which was a little curved and with a groove on each side. The
fangs of others were weathered, not grooved, curved and acute." Cope, 1867.Occurrence. Calvert formation. Charles
County near the Patuxent river. Collections. The type is in the Museum
of the Academy of Natural Sciences of Philadelphia.

Description. "One of
the teeth (pl. xxx, fig. 10) bears a resemblance to the first described of the
large species (mento).
"Its crown is proportionately longer, and
the posterior tubercle and internal curved ridge of the crown are rudimental,
but it has the same general form, with the abrupt curvature and slight twists
of the summit backward and inward. The ridges defining the inner and outer surfaces
of the crown are alike in their course and the enamel is likewise wrinkled.
"The crown has the same form but is comparatively
less curved.
"Length of fang 5 lines (10 mm.); breadth
3.75 lines (7.5 mm.); thickness 3 lines (6 mm.)"

Occurrence. Calvert formation. Charles
County near the Patuxent river. Collection. The type is in the Museum
of the Academy of Natural Science of Philadelphia.

Family PHYSETERIDAE.

Teeth entirely absent in the upper jaw and quite
variable in the mandible, either numerous as in the sub-family PHYSETERINAE,
or reduced even to a single tooth in each jaw as in some of the ZIPHIINAE.
In both of these families the bones of the cranium posterior to the nares form
an elevated crest that converts the facial region into a considerable concavity,
it is in this concavity that the oily material from which spermaceti is refined
finds lodgement. Physeter, Mesoplodon and Hyperoodon are
living members of this family.

Genus Obycterocetus
Leidy.

Cope in 1867 thus characterizes the genus. "Obycterocetus
Leidy. This genus differs from Physeter in the extensive pulp cavity
of the teeth, and the absence of the surface cementation."

Description. "This species
is based on a tooth belonging to an individual of one-third or one-fourth the
size of the known species, O. cornutidens Leidy, but nevertheless adult,
as attested by the obliquely worn apex of the crown. The general form is that
of an elongate curved cone, with flattened sides, and a broad convex face within
the curve, and a narrower one on the outside. The tooth is marked by numerous
irregular transverse lines, similar to those frequently marking growth, and
by longitudinal shallow grooves. The pulp-cavity extends for two-thirds the
length of the tooth, being thus relatively deeper than in the known species,
and is also very large, thinning the external wall out to an open basis. In
the known species the walls are relatively thicker, and for a considerable distance
parallel to each other. The form of the tooth is in some degree similar to the
crown of the canines of some crocodiles. There is no enamel on the teeth of
Cetaceans of this genus.
"Total length, 2 inches, 5 lines; long diameter
at base, 8.25 lines; diameter at middle, 6 lines." Cope, 1867.
In 1869 Leidy repeats the characters of O.
cornutidens: "conical, strongly curved, and proportionately much broader
approaching the base than in the preceding species [O. quadratidens]
; nor does it assume a quadrate appearance, but is nearly circular or ovoidal
in transverse section. The deep conical pulp cavity is defined by a sharp edge
at the periphery of the base."
In this article Leidy remarks that Cope's O.
crocodilinus is most likely a young individual of O. cornutidens,
also he says that in the light of the great variability in the teeth of the
PHYSETERIDAE in general that he regards it as very possible that all
three species, described from teeth, belong to the same species.Occurrence. Calvert formation. Charles
County near the Patuxent river. Collection. Cope's type of O.
crocodilinus is in the Museum of the Academy of Natural Sciences of Philadelphia.

1 This
and the following genus, founded on teeth, are regarded by Cope as belonging
to the PLATANISTIDAE but by Zittel as possibly belonging In the anterior
series of some member of the SQUALODONTIDAE. The discovery of a more
complete dentition, only, can settle this question. Cope's classification seems
the most probable.